Audi Audi S4 2016-present Exhaust System Bolt Torque Specifications & Gasket Sealing
Audi Audi S4 2016-present

Audi Audi S4 2016-present Exhaust System Bolt Torque Specifications

Detailed torque specifications for all exhaust system bolts on the 2016-Present Audi S4 (B9 and B9.5 generations). Includes downpipe, mid-pipe, and rear exhaust sections.

Updated

Important Information

Safety guidelines and reference information for proper torque application

Quick Reference Guide
ft-lbs → Nm
× 1.356
ft-lbs → kg-m
× 0.138
Nm → ft-lbs
× 0.738
in-lbs → ft-lbs
× 0.083

Common Torque Patterns

Star Pattern

Used for wheels and other circular bolt patterns

Star Pattern torque pattern diagram showing proper bolt tightening sequence
Cross Pattern

Used for gaskets and cover plates

Cross Pattern torque pattern diagram showing proper bolt tightening sequence
Sequential Pattern

Used for head bolts and other critical components

Sequential Pattern torque pattern diagram showing proper bolt tightening sequence

Common Mistakes to Avoid

Over-tightening

Exceeding the specified torque value can stretch or break fasteners, damage threads, or crack components.

Prevention:

Always use a calibrated torque wrench and follow specifications exactly.

Incorrect Torque Sequence

Tightening bolts in the wrong order can cause uneven pressure distribution and potential leaks or damage.

Prevention:

Follow the manufacturer's specified torque sequence pattern.

Dirty Threads

Dirt, rust, or old thread locker can affect torque readings and proper fastener tension.

Prevention:

Clean and inspect all threads before assembly. Use new thread locker if specified.

Reusing TTY Bolts

Torque-to-yield bolts are designed to stretch and must not be reused.

Prevention:

Always replace TTY bolts with new ones. They are single-use only.

Dry vs. Lubricated

Not accounting for whether torque specs are for dry or lubricated fasteners can lead to incorrect tension.

Prevention:

Check if specs are for dry or lubricated threads. Use specified lubricant when required.

Recommended Tools

Torque Wrench (1/4" Drive)

Range: 2-25 ft-lbs
Small fasteners, delicate components

Torque Wrench (3/8" Drive)

Range: 10-100 ft-lbs
Most common automotive fasteners

Torque Wrench (1/2" Drive)

Range: 30-250 ft-lbs
Large fasteners, wheels

Angle Gauge

Torque-to-yield (TTY) bolts

Torque Wrench Care

  • Calibrate annually or after 5,000 clicks
  • Store at lowest setting
  • Keep clean and lubricated

Search Specifications

Search by component name, bolt size, or description

Torque Calculator

Convert between different torque units

Turbo Downpipe

This section covers the critical connection points between the turbocharger(s) and the downpipes, where high temperatures and pressures are present. Proper torque is crucial to prevent exhaust leaks and ensure performance.

1

Downpipe to Turbocharger Flange Bolts/Studs

M10 x 1.5
Torque Value
30 ft-lbs (40 N·m)
Important Notes
These fasteners secure the downpipes directly to the turbocharger outlet. Correct torque is critical to prevent exhaust leaks at this high-pressure point. Estimated based on similar Audi models.

Midpipe Connections

This section pertains to the connections between the downpipes and the mid-pipe section of the exhaust system. Proper torque at these joints is crucial to prevent exhaust leaks and maintain correct exhaust flow.

1

Downpipe to Mid-Pipe Flange Bolts

M10 x 1.5
Torque Value
30 ft-lbs (40 N·m)
Important Notes
These connect the downpipes to the rest of the exhaust system. Proper torque here is important to prevent leaks and maintain proper exhaust gas flow. Estimated based on similar Audi models.
2

Mid-pipe Clamps

M8 x 1.25
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Clamps hold the exhaust pipes together. These rely on proper clamping force to ensure a leak-free seal by creating tension between pipe surfaces. Proper torque prevents crushing the pipes or slipping. Estimated based on similar Audi models.

Exhaust Hangers

This section details the torque specifications for the bolts that secure the exhaust system to the vehicle's chassis and the exhaust pipes via hangers. Correct torque here is vital for preventing excessive movement and damage to the exhaust system.

1

Exhaust Hanger Bracket Bolts (Chassis side)

M8 x 1.25
Torque Value
18 ft-lbs (24 N·m)
Important Notes
These bolts secure the exhaust hanger brackets to the vehicle's chassis. Correct torque is necessary to prevent the exhaust system from excessive movement. Estimated based on similar Audi models.
2

Exhaust Hanger Bracket Bolts (Exhaust side)

M8 x 1.25
Torque Value
18 ft-lbs (24 N·m)
Important Notes
These bolts secure the exhaust hangers to the exhaust pipes. Proper torque ensures the exhaust system is securely held in place. Estimated based on similar Audi models.
3

Rear Muffler Hanger Bolts (To vehicle body)

M8 x 1.25
Torque Value
18 ft-lbs (24 N·m)
Important Notes
These secure the rear muffler hangers to the car's chassis. Similar to the other hanger bolts, they are critical for maintaining exhaust system position. Estimated based on similar Audi models.

Muffler Connections

This section describes the torque for bolts that connect the muffler to the rest of the exhaust system.

1

Muffler Inlet Flange Bolts

M8 x 1.25
Torque Value
22 ft-lbs (30 N·m)
Important Notes
These bolts attach the muffler to the mid-pipe or resonator. Maintaining a proper seal is important for sound management and preventing leaks. Estimated based on similar exhaust connections in Audi models.

Electrical Grounding

This section covers the torque specification for the exhaust system ground strap. Proper torque here ensures adequate electrical contact.

1

Exhaust System Ground Strap Bolt

M6 x 1.0
Torque Value
8 ft-lbs (11 N·m)
Important Notes
This bolt secures the ground strap to the exhaust system. Although not a structural fastener, this is important for electrical grounding and should be torqued correctly to ensure proper contact and prevent electrical issues. Estimated based on common grounding strap specifications.

O2 Sensor

This section covers the torque specification for the lambda/O2 sensor. Proper torque ensures sealing of the exhaust system and prevents leaks.

1

Lambda/O2 Sensor

M18 x 1.5 (Sensor Thread)
Torque Value
30 ft-lbs (40 N·m)
Important Notes
Lambda or O2 sensor proper torque ensures the sensor is properly seated, sealing the exhaust system and preventing leaks, which will ensure accurate readings. It is critical to avoid crushing the sensor during installation. Industry standard torque for O2 sensors.

Troubleshooting Guide

Common issues, diagnostic steps, and prevention guidelines

Common Issues

Bolt stretching, stripped threads, uneven torque patterns

Loose Components

Symptoms:
  • Rattling or vibration noises
  • Visible movement in components
  • Uneven panel gaps
Solutions:
  • Clean threads and mounting surfaces
  • Replace damaged fasteners
  • Apply proper torque in sequence
  • Use thread locker if specified

Stripped Fasteners

Symptoms:
  • Unable to achieve proper torque
  • Fastener spins freely
  • Visible thread damage
Solutions:
  • Use thread repair kit if appropriate
  • Install thread insert (HeliCoil)
  • Replace component if threaded hole is damaged
  • Upgrade to higher grade fastener if recommended

Overtightened Components

Symptoms:
  • Cracked or deformed parts
  • Broken fasteners
  • Compressed gaskets or seals
Solutions:
  • Replace damaged components
  • Use new fasteners
  • Follow proper torque sequence
  • Verify correct torque specifications

Diagnostic Steps

Visual inspection, torque verification, thread assessment

1

Visual Inspection

Inspect the affected area for any visible signs of damage or wear

  • Check for cracks or deformation
  • Look for signs of excessive wear
  • Verify proper fastener installation
2

Torque Verification

Verify the torque applied to the fasteners

  • Check the torque wrench calibration
  • Verify the torque specification
  • Compare the applied torque to the specification
3

Thread Assessment

Assess the condition of the threads

  • Check for signs of thread damage
  • Verify the thread type and size
  • Check for proper thread engagement

Prevention Guidelines

Best practices, maintenance tips, tool care

Best Practices

  • Always follow the recommended torque specification
  • Use the correct type and size of fasteners
  • Verify the torque wrench calibration regularly

Maintenance Tips

  • Regularly inspect the affected area for signs of wear or damage
  • Replace damaged or worn-out components promptly
  • Keep the work area clean and organized

Tool Care

  • Regularly clean and maintain the torque wrench
  • Store the torque wrench in a dry and secure location
  • Verify the torque wrench calibration before each use

Frequently Asked Questions

Find answers to common questions about torque specifications

Q1

What happens if I overtighten exhaust bolts?

Overtightening can stretch or break the bolts, damage the threads in the exhaust flanges, and lead to exhaust leaks. This can result in a noisy exhaust, reduced performance, and potential damage to other components due to heat and exhaust gas exposure. For example, overtightening downpipe bolts could warp the flange and require a new downpipe.

Q2

What happens if I under-tighten exhaust bolts?

Under-tightening exhaust bolts will almost certainly cause exhaust leaks. This results in a noisy exhaust, poor performance, and the possibility of hot exhaust gases damaging nearby components, such as the undercarriage. The vibrations from the exhaust system could also cause loose bolts to fall out, creating potentially dangerous situations while driving.

Q3

Should I use new gaskets when reinstalling my exhaust?

Yes, absolutely. Exhaust gaskets are designed to crush and seal between exhaust components. They should not be reused as they will not provide a proper seal, which can lead to exhaust leaks. When installing an exhaust, the safest practice is to always use new gaskets each time they are separated.

Q4

Should I use anti-seize on exhaust bolts?

Yes, using anti-seize on exhaust bolts is highly recommended. The extreme heat cycles that exhaust systems endure can cause bolts to seize and become difficult to remove later. Applying a thin layer of anti-seize will help prevent this issue when performing routine maintenance, or any future removal of exhaust components. Always use an anti-seize compound rated for high temperatures.

Q5

How often should I check my exhaust bolt torque?

It's a good practice to check exhaust bolt torque after the initial installation and then again after a few hundred miles or a few heat cycles. This is especially important after installing new aftermarket exhaust components. After that, you should routinely check them during normal service intervals or when you notice an exhaust leak.

Environmental Considerations

Temperature, humidity, and seasonal effects on torque specifications

Temperature Effects

Includes: High Heat, Cold Weather, Thermal Cycling

Temperature can significantly impact torque values and fastener behavior

Cold Weather

Effects:
  • Increased material brittleness
  • Higher torque required due to thread contraction
  • Reduced thread lubricant effectiveness
Recommendations:
  • Allow components to warm to room temperature when possible
  • Consider using winter-grade thread lubricants
  • Check torque values more frequently during winter months

Hot Weather

Effects:
  • Thermal expansion of components
  • Decreased friction in threads
  • Accelerated lubricant breakdown
Recommendations:
  • Check torque when components are at normal operating temperature
  • Use temperature-resistant thread lockers
  • Consider re-torquing after heat cycles

Humidity and Corrosion

Covers: Rust Prevention, Salt Exposure, Moisture Control

Moisture and corrosion can affect fastener integrity and torque values

High Humidity

Effects:
  • Accelerated corrosion formation
  • Reduced friction coefficient
  • Potential thread seizing
Prevention:
  • Use corrosion-resistant fasteners
  • Apply appropriate anti-seize compounds
  • Maintain proper protective coatings

Salt Exposure

Effects:
  • Rapid corrosion development
  • Thread damage
  • Seized fasteners
Prevention:
  • Regular underbody washing
  • Use of sacrificial anodes where appropriate
  • Application of protective coatings

Seasonal Maintenance

Spring, Summer, Fall, and Winter maintenance schedules

Spring

  • Inspect for winter damage
  • Clean and protect exposed fasteners
  • Check torque on critical components

Summer

  • Monitor heat-affected components
  • Check expansion-related loosening
  • Inspect cooling system mounts

Fall

  • Prepare for winter conditions
  • Apply corrosion protection
  • Verify all fasteners are properly torqued

Winter

  • More frequent inspection of critical fasteners
  • Check for salt damage
  • Monitor suspension component torque

Related Resources

Tools, service procedures, and technical bulletins

Recommended Tools

Torque Wrench (1/2 inch drive)

A calibrated torque wrench capable of measuring torque values within the specified range for exhaust bolts.

  • Measures torque in Newton-meters (Nm) or foot-pounds (ft-lbs)
  • Click-type or digital display for accurate readings
  • Range typically 20-100 Nm
Learn more

13mm Socket (1/2 inch drive)

A standard 13mm socket designed for use with a 1/2 inch drive torque wrench, necessary for removing and tightening exhaust bolts.

  • 6-point socket for secure grip
  • Impact-rated recommended, but not essential for manual tightening
  • Chrome Vanadium Steel construction
Learn more

16mm Socket (1/2 inch drive)

A standard 16mm socket designed for use with a 1/2 inch drive torque wrench, necessary for removing and tightening exhaust bolts.

  • 6-point socket for secure grip
  • Impact-rated recommended, but not essential for manual tightening
  • Chrome Vanadium Steel construction
Learn more

Anti-Seize Lubricant

A lubricant applied to the threads of exhaust bolts to prevent seizing and facilitate easier removal in the future.

  • High-temperature resistance
  • Prevents corrosion and galling
  • Reduces the chance of breaking bolts upon removal
Learn more
Service Procedures

Exhaust Downpipe Bolt Torque Procedure

Procedure for correctly torquing the bolts connecting the downpipes to the turbochargers on a 2016-Present Audi S4 (B9/B9.5).

  • Locate the bolts connecting the downpipes to the turbochargers.
  • Apply a small amount of anti-seize lubricant to the threads of each bolt.
  • Install bolts by hand until snug
  • Using the torque wrench and 13mm socket, torque each bolt to 40Nm.
  • Perform a final check to ensure all bolts are tightened to spec
View full procedure

Exhaust Clamp Bolt Torque Procedure

Procedure for correctly torquing the exhaust clamp bolts between the downpipe and cat-back exhaust system on a 2016-Present Audi S4 (B9/B9.5).

  • Locate the exhaust clamp bolts between downpipe and catback
  • Apply a small amount of anti-seize lubricant to the threads of each bolt.
  • Install bolts by hand until snug.
  • Using the torque wrench and 13mm socket, torque each bolt to 25Nm.
  • Perform a final check to ensure all bolts are tightened to spec.
View full procedure

Exhaust System Mounting Bracket Bolt Torque Procedure

Procedure for correctly torquing the bolts holding the exhaust system mounting brackets to the chassis of a 2016-Present Audi S4 (B9/B9.5).

  • Locate the exhaust system mounting bracket bolts.
  • Apply a small amount of anti-seize lubricant to the threads of each bolt.
  • Install bolts by hand until snug.
  • Using the torque wrench and 16mm socket, torque each bolt to 55Nm.
  • Perform a final check to ensure all bolts are tightened to spec.
View full procedure
Technical Service Bulletins

Exhaust Bolt Corrosion Concerns

2018-03-15

Reports of excessive corrosion on exhaust bolts, specifically in regions with harsh climates or road salt usage.

2016-2018

Resolution: Apply anti-seize lubricant during installation or maintenance of the exhaust system. Replace corroded bolts as needed.

Loose Downpipe Bolt Issues

2020-07-22

A small number of reports have indicated that downpipe bolts can loosen over time due to thermal cycling. Periodic checks recommended.

2016-2020

Resolution: Re-torque downpipe bolts to specified torque (40Nm) during routine maintenance intervals.

About the Author

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Alan Montanye - Automotive Technical Specialist
ASE

Alan Montanye

Automotive Technical Specialist

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